1. Field of the Invention
The present invention relates to a battery with a nonaqueous electrolyte, and more particularly to a battery with a nonaqueous electrolyte, using an improved negative electrode active material.
2. Discussion of the Background
In recent years, rechargeable batteries with a nonaqueous electrolyte, using a lithium metal, a lithium alloy, a lithium compound, a carbon material or the like as a negative electrode active material have been expected as batteries with high energy density, and the research and development of these batteries are currently being energetically done. Up to now, lithium ion batteries using LiCoO2, LiMn2O4 or the like as the positive electrode active material and a carbon material, capable of occluding and releasing lithium, as the negative electrode active material have been extensively put to practical use.
On the other hand, rechargeable batteries using a lithium metal, a lithium alloy, or a lithium compound as the negative electrode active material have been expected to have high capacity. They, however, have not yet been put to practical use. The reason for this is mainly that the use of the lithium metal leads to a deterioration of lithium as a result of a reaction of a nonaqueous electrolysis solution with the lithium metal and, in addition, the elimination of lithium due to the occurrence of dendritic lithium upon the repetition of discharge and charge and thus poses problems of internal short circuit and short cycle life. In order to solve these problems, studies have been made on the use of lithium alloys or lithium compounds as the negative electrode. In particular, in lithium-aluminum or other alloys, the reactivity with the nonaqueous electrolysis solution can be reduced to improve the charge and discharge efficiency. In this case, however, the repetition of a high level of discharge and a high level of charge causes crumbling of the electrode. Therefore, an improvement in cycle life characteristics is unsatisfactory.
Further, the use of chalcogen compounds, such as oxides, as the negative electrode active material has been proposed from the viewpoint of increasing the capacity in the negative electrode (for example, SnO and SnO2; see Japanese Patent Laid-Open Nos. 122274/1995). Further, a proposal has been made to use amorphous oxides, such as SnSiO3 or SnSi1xe2x88x92xPxO3, to improve cycle characteristics (see Japanese Patent Laid-Open No. 288123/1995). At the present time, however, even these chalcogen compounds could not have simultaneously improved the cycle life characteristics and the capacity to a satisfactory level.
The present invention has been made with a view to solving the above problem of the prior art, and it is an object of the present invention to provide a battery with a nonaqueous electrolyte, which possesses a combination of high capacity with excellent cycle life, through the use of a negative electrode active material possessing a high capacity and excellent charge-discharge cycle characteristics.
According to one aspect of the present invention, there is provided a battery with a nonaqueous electrolyte, comprising: a positive electrode; a negative electrode having a negative electrode active material capable of occluding and releasing an alkali metal; and a nonaqueous electrolyte, said negative electrode active material containing at least one element selected from the group consisting of group 4B elements and group 5B elements and having at least one crystal structure selected from the group consisting of BiF3 structure, Cu2MnAl structure, and AgAsMg structure. Above 4B elements and group 5B elements are selected from the group consisting of Si, Ge, Sn, P, Sb and Bi. Since Al does so the same effect as Sb, it can be replaced with and adopted as Sb. So the negative electrode can be contained the active material, the active material containing at least one element selected from the group consisting of Al, Si, Ge, Sn, P, Sb and Bi, and the active material having at least one crystal structure selected from the group consisting of BiF3 structure, Cu2MnAl structure and AgAsMg structure.
According to an embodiment of the present invention, the negative electrode active material further contains an alkali metal.
The above negative electrode active material can occlude a large amount of an alkali metal such as lithium, and, at the same time, has high reversibility between an occlusion reaction and a release reaction and can solve the problem of crumbling involved in charge-discharge cycles. Thus, this negative electrode active material can realize a negative electrode possessing a long life and a high capacity. These advantageous characteristics are derived from the fact that the negative electrode active material according to the present invention is a structurally stable material which, even after the occlusion of a large amount of an alkali metal, can maintain the basic crystal structure.
In particular, from the viewpoints of both high capacity and long life, the crystal structure preferably comprises at least one member selected from the group consisting of BiF3 structure, Cu2MnAl structure, and AgAsMg structure, and, more preferably, the negative electrode active material further contains an alkali metal from the viewpoint of long service life.
Further, at least one element selected from the group consisting of Al, Si, Ge, Sn, P, Sb and Bi is preferably contained from the viewpoint of high capacity. In particular, the negative electrode active material preferably contains antimony as an indispensable component.